1. Field of the Invention
The present invention is directed to stable, aqueous dispersions of polyurethane-ureas containing chemically incorporated anionic groups which are neutralized with a mixture of volatile and nonvolatile cations.
2. Description of the Prior Art
The production of linear or cross-linked, aqueous, polyurethane-urea dispersions is known as shown by U.S. Pat. Nos. 3,479,310; 4,066,591; 4,092,286; 4,108,814; 4,237,264; and 4,238,378 which disclose linear polyurethane-ureas and U.S. Pat. Nos. 3,870,684 and 4,203,883 as well U.S. Pat. No. 4,408,008, issued Oct. 4, 1983, which disclose cross-linked polyurethane-ureas. The aqueous polyurethane-urea dispersions may be used for a wide range of commercial applications such as adhesives or coatings for various substrates including textile fabrics, plastic, wood, glass fibers and metals. Chemical resistance, abrasion resistance, toughness, tensile strength, elasticity and durability are among the many desirable properties of these coatings. In some cases these properties of coatings prepared from aqueous polyurethane-urea dispersions have equaled or even surpassed the performance levels of coatings obtained from solvent-based polyurethane lacquers.
However, one property of coatings prepared from aqueous polyurethane-urea dispersions which need to be improved in order to match the performance of coatings prepared from solvent-based polyurethane lacquers is the hydrolytic stability. This property is adversely affected by the hydrophilic materials necessary for ensuring the dispersibility of the polyurethane-ureas in an aqueous medium.
Accordingly, it is an object of the present invention to provide aqueous polyurethane-urea dispersions which may be used to prepare coatings having improved hydrolytic stability.
It is an additional object of the present invention to provide aqueous polyurethane-urea dispersions which may be used to prepare coatings having excellent chemical resistance, abrasion resistance, toughness, tensile strength, resistance to water swell, elasticity and durability.
Surprisingly, it has been found that these objectives may be achieved according to the present invention as hereinafter described.